Field of the Invention
The present invention relates generally to pneumatic valve actuators and, more particularly, to pneumatic valve actuators utilizing methods and devices for force multiplication in the actuation process.
Pneumatically actuated valves are commonly used to control the flow of fluids where remote operation is desired. Examples include utilization in automated processes and hazardous locations. Pressurized air supplying systems for pneumatic controls are typically limited to a maximum pressure of 80-100 psig. Because of this low pneumatic control pressure, pneumatic valve actuators, and especially those that control high pressure fluids through an associated valve, are typically very large in physical size. The large size is necessary to provide a sufficiently large surface area upon which the pneumatic pressure works to generate the force required to control the flow of fluid through the associated valve. At higher fluid pressures, a proportionally higher force is needed to maintain control.
Typical pneumatic valve actuators consist of single and multiple piston designs. Pneumatic pressure acting on the exposed surface area of the piston(s) determines actuator force. Pneumatic valve actuators, and particularly the larger size actuators, pose problems for system designers of fluid distribution systems. Due to exhaust requirements, space constraints, and other relevant factors, it is greatly desirable to minimize the physical size of these pneumatic valve actuators without reducing their ability to generate actuation force or sacrifice valve performance.
Known actuators are disclosed in U.S. Pat. Nos. 4,684,103; 4,875,404; and 5,253,671 wherein attempts have been made to reduce the actuator""s size by utilizing a force multiplication mechanism to enable the generation of high forces relative to actuator size. Although the size of these actuators is somewhat reduced, the reductions in size come with inherent disadvantages. The force multiplying mechanism in each of these actuators consumes a substantially large portion of the actuator size and resultantly limits the overall size reduction permitted of the actuator. Also, the force multiplying mechanism in each of these actuators requires an increase in the number of moving parts within the actuator. These additional moving parts increase actuator complexity and decrease its overall reliability.
U.S. Pat. No. 6,059,259 successfully addresses the above described deficiencies, but is more complex than the present invention which has purposely been developed as a simplified solution to the need for size reduction.
Surround-type lever applications, such as a conical-type lever, have proved helpful, but overall unsuccessful because of strength and flexibility inadequacies. A traditional surround-type disk lever is used by applying an actuating force to one side of the disk proximate an interior or exterior edge to pivot the opposite edge about a fulcrum that is located along the opposite surface of the disk. Such a lever has an actuating benefit of allowing application of the actuating force over a large area. A levering benefit, generic to all lever applications, is accomplished via creation of an output levering force that is a multiple larger than the actuating force. Such efforts have proved unsuccessful for high-pressure, small space, applications because arrangements with sufficient flexibility for surround-type levering do not have the strength or rigidity required to actuate the applicable higher pressure valves. Conversely, levers with sufficient strength and rigidity often do not have the flexibility required to accommodate the configuration changes necessary for surround-type levering.
The arrangement of the present invention has been developed in response to these drawbacks which have been appreciated in the art, and as well to provide further benefits to the user. These enhancements and benefits are described in greater detail herein below with respect to several alternative embodiments of the present invention.
The present invention alleviates the drawbacks described above with respect to known pneumatic force multiplication actuator devices by employing a serpentine disk lever that has the strength and flexibility required for high pressure applications. The present invention is disclosed in several embodiments and incorporates beneficial features in addition to those just stated as will be described herein below.
Generally, the present invention provides a disk that is flexible enough to be used as a surround-type lever while also being strong enough to accommodate high force transmission requirements, such as those present in high pressure valve systems. The high strength of the disk is accomplished through using a hard material and a specified shape. An example of an applicable hard material of construction is hardened steel. A preferred shape of the disk is circular, whereby the stresses experienced in the disk during use are endeavored to be evenly distributed throughout the disk. The flexibility requirement of levering with a disk, or surround-type levering, is accomplished by the particular cutting of the disk, which will be described in detail.
Benefits of this disk lever configuration, in addition to substantial strength and flexibility increases, permits a smaller and lighter disk arrangement, conservation of construction material, and increased durability. A smaller sized lever is now possible because of the ability to utilize a much stronger material. A weaker material would necessitate use of a disk of significantly greater dimensions to accommodate equal force requirements. A lighter weight disk is possible in the present invention because of the extraction of material to form the mentioned cuts, or slits. Similar benefits may also be provided, if during original formation of the disk, voids are provided where the cuts and slits have been prescribed. A lighter disk lowers the burden on disk production, disk transportation, and on the incorporating system of the disk. Conservation of material is possible by way of recycling the excess material created during the slit cutting process. In this way, the same amount of disk levers can be created from a lower amount of material. The durability, or robustness of the disk is increased by way of the material used, the disk shape, and the type and configuration of the cuts made in the disk. Each of these aspects contribute to minimizing stress concentrations, as well as withstanding those stresses that are induced during operation.
A particularly preferred utilization of the serpentine disk is as a lever in a valve actuator assembly. The purpose of a valve actuator is to open or close an associated valve. This opening and closing of the valve is typically accomplished by the action of a valve stem. While a spring in the actuator continuously works to force the valve stem toward the fully closed position, the disk lever, when actuated, works against this spring to force the valve stem toward the fully open position.
In one embodiment, the serpentine disk lever of the present invention is manufactured to have an outer, or external, and an inner, or internal, edge. Regarding one exemplary embodiment, when the actuator is in the closed position, the lever takes the form of a traditional disk having a planar, flat shape. The disk is located in the valve actuator housing so that it contacts a piston near its external edge. The location of this contact can be called the actuating location. The disk also contacts the valve stem near its internal edge. The location of this contact can be called the lifting location. Finally, to create a levering system, the disk rests on a fulcrum. The location of the contact between the disk and fulcrum lies somewhere between the actuating and the lifting locations just mentioned. The fulcrum location is preferably located closer to the lifting location and the precise force multiplicating effect of the lever is affected by the exact location of the fulcrum. In operation, after the piston applies a downward force on the external edge of the disk, the disk pivots about the fulcrum to push the valve stem toward a fully open position or configuration. This action transforms the serpentine disk from a flat configuration to a frusto-conical configuration when considering a round serpentine disk.
As mentioned, a circular and hard disk with cuts made into it is a preferred embodiment for providing the strong and flexible disk needed in compact, high pressure, and surround-type lever applications. The disk is cut, by laser for example, to have a serpentine portion. A serpentine shape is created by making alternating cuts, or slits, into the disk from the interior and external edges. In this way, each internal cut, except for those that are at the end of a serpentine pattern, is disposed between a pair of external cuts, and visa versa. Such alternating cutting forms a general zigzag pattern, which as the name serpentine intimates, resembles a snake that has its body going back and forth on the ground. Therefore, if a person was to follow or trace the continuous material that forms the serpentine pattern with their eye or finger, they would have to travel back and forth through the windings that are formed. Such a winding trace would be required because there is no connection between the legs of the serpentine pattern besides those proximate the internal and external extremities of the disk. In the flat-disk configuration, the extremes, where the legs of the windings are connected, are alternatively located near the internal and external edges of the disk. This and other aspects of the invention will become more apparent upon review of the entire disclosure, and especially when the figures are considered.
A properly created serpentine pattern will allow for the flexibility required for the disk to transition from its flat, planar shape, to its conical shape, while not compromising the strength required for high pressure levering applications. The flexibility is created because the several legs of the serpentine pattern will be able to move with respect to each other. This relative movement will occur as the legs are allowed to flex at the mentioned connection points located at the internal and external edges of the disk. Disk flexing is possible because of the absence of material, or spaces between the legs. Specifically, when a flat round disk is flexed into a frusto-conical shape, the material at the internal edge of the disk will have a tendency toward spreading out as the aperture created by the inner hole becomes larger because of the cone shape being formed. At the same time, the material around the external edge will have a tendency to move closer together as the external edge becomes smaller as the cone shape is being formed. As will be described in further detail, it is the slits, and the specific shape and orientation of these slits, that allows for the disk to flex as required while not compromising levering capability.
As mentioned before, a more flexible material can be used instead of the hard material with serpentine cuts prescribed by the present invention. Unfortunately though, a material flexible enough to allow levering from a flat shape to a cone shape without the relief aspects of the described cuts or voids cannot also be strong enough to impose a very great lifting force at the lifting edge. Instead of lifting, for example, the softer disk will likely and undesirably bend about the fulcrum point when levering is attempted. Conversely, the overall strength or radial rigidity of a disk with the prescribed serpentine design is maintainable based on the shape of the cuts, or slits. In effect, each of the radial legs formed between the radial cuts in the disk will work as an individual lever. In this way, twenty legs effectively work like twenty separate levers.
In one embodiment, the disk lever of the present invention has more than one portion with a serpentine configuration. A benefit of having multiple serpentine shaped portions in a disk is a corresponding increase in flexibility. For locating the serpentine portions, a user may depend on variables such as the location of the actuating force being applied to the disk lever, the location of the lifting force resulting from levering, and the shape of the disk being used.
In a particularly preferred embodiment, a serpentine pattern according to the present invention is cut into the entirety, or almost the entirety of the disk lever. In this embodiment, external slits are cut inwardly into the disk from the entirety of the outside perimeter or external edge and internal slits are cut outwardly into the disk about the entirety of the inside perimeter or internal edge. Given that each internal slit is disposed between adjacent external slits in this configuration, a pattern is established around the disk that alternates between internal and external slits. Flexibility is high in this embodiment because the disk is capable of adjusting the configuration of its inner edge (getting a bit larger) and its outer edge (getting a bit smaller) as the disk transitions about the fulcrum from a flat shape to a frusto-conical shape.
In the illustrated embodiment, the internal slits of the serpentine disk are disposed intermediate, or midway between, adjacent external slits. This characteristic can be utilized when the entire disk is serpentine, when many portions of the disk are serpentine, or even when only one portion of the disk is serpentine. As a compliment, each external slit is disposed intermediate adjacent internal slits. In this configuration, each external slit is disposed intermediate adjacent internal slits, and visa versa, so that the serpentine pattern formed about the disk is uniform. For embodiments in which the entire disk is serpentine, the pattern extends around the entirety of the disk.
As will be appreciated by those familiar with the art, disk strength is compromised when stress is allowed to be focused in certain parts of the disk because of the increased likelihood that a fracture or failure will occur at that location. The symmetry that results from the uniform cutting of a circular disk is important to strength maintenance because of the lower tendency for stress concentration.
In yet another embodiment or variation, the internal and external slits are cut in specified ways that further maximize flexibility and limit stress concentrations. As an example, the external slits may be formed to be twice as wide as the internal slits, and each type of slit designed to terminate in a round-shaped closed end. The internal and/or external slits may be further enhanced by adding a bulbous aperture at the terminal end of the slits. Although specific examples of slit cutting are given, such as laser cutting, it will be appreciated by those skilled in the art that other ways of shaping the disk will be obvious to implement.
Having the external slits twice as wide as the internal slits promotes strength and flexibility. Although a disk that is transitioned from a flat shape to a frusto-conical shape experiences noticeable flex at both its external and internal edges, much greater flex is necessary at the external edge. Wider slits at the external edge help to accommodate this greater flex. Additionally, although the disk can have wider internal slits than those shown, smaller slits are sufficient for the lower flexibility needed at the internal edge. Furthermore, having the internal slits thinner promotes greater strength by allowing for more disk material to be present.
Having rounds or bulbous apertures at the extreme, or distal, internal or terminating ends of some, or all of the internal and external slits promotes operational strength and rigidity. The ability for stress to concentrate is lowered by having significant, continuous, or bulbously defined slit terminations.
Regarding the bulbous apertures that may be formed in the distal ends of the slits, the radius of the bulb-portion can be advantageously a multiple greater than one and one-half of the width of appended slit. The bulbous apertures distribute stress over a larger surface; that is, the edge of the bulb, than would be otherwise possible when only a radius equal to half the width of the corresponding slit is used. Further advantages of having a bulb portion are that less material is utilized in the disks"" production and lighter disks thereby result.
The beneficial effects described above apply generally to the pneumatic actuator of the present invention and its several possible embodiments. An exemplary structure through which these benefits may be delivered is described in detail herein below.